Process of preparing bright yellow colored phosphorus sulfide



Feb., 25, 1958 .1. w. LEFFORGE 2,824,788

PROCESS OF PREPARING BRIGHT YELLOW COLORED PHOSPHORUS SULF IDE Filed July 23, 1954 2/ J n50/0M 4 J l r Zz A/ 7L- 2 I warez m0/o Z4 0 .501. Fae fw/51. Fara 7mm Z #Z 2 1 z UZ 1 Z 7 asr 30? 3e/NOMI@ cauzcrae MILL INVENTOR JOHN n. foms ATTORNEY PROCESS F PREPARHNG BRIGHT YELLOW CLGRED PHSPHRUS SULFIDE John W. Letorge, Danvers, Mass., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware Application July 23, 1954, Serial No. 445,349

6 Claims. (Cl. 23-206) This invention relates to phosphorus suliides and to an improved method of producing same.

Heretofore, phosphorus suldes have been prepared continuously by introducing phosphorus and sulfur with agitation into a molten heel of phosphorus sulfide and reacting these materials in the proportions calculated to yield the desired product. ln carrying out this reaction, the exothermic heat is absorbed by the molten heel of phosphorus sulfide and thereby transferred to a suitable heat exchanging material or surface. The product of this reaction is withdrawn continuously from the reaction zone, flaked on chill rolls and then converted into a powder by grinding in a hammer mill or equivalent pulverizing device. This method provides a means of producing phosphorus suldes continuously but is subject to certain disadvantages which render the method and product commercially unattractive,

For example, this method invariably yields darkly colored products as a result of the accumulation of impurities including those derived from the raw materials and the metal equipment. The color of these materials can be improved to some extent by distillation, but until the development of the invention disclosed and claimed in the application Serial No. 445,329, tiled luly 23, 1954, such treatment has involved the use of additional heat and equipment, all of which add substantially to the overall cost of manufacturing these products.

Another disadvantage of this method is that if the phosphorus and sulfur feeds vary from a predetermined rate, the resulting product has a heterogeneous composition due to the presence of excess reactants or the formation of phosphorus suldes other than the one desired.

in an application assigned to the same assignee as the instant application Serial No. 445,329, tiled iuly 23, 1954, which has issued as Patent No. 2,794,705, lune 4, 1957, a method of producing phosphorus suldes of improved color is disclosed and claimed. in accordance with this method phosphorus and sulfur are introduced continuously into a boiling mass of phosphorus suldes so as to effect a continuous reaction between the phosphorus and sulfur and continuous distillation of the reaction product. From the standpoint of economy of operation, simplicity of equipment, color improvement of product and product uniformity, this method represents a substantial advance in the art over the method previously described herein. However, it is not possible by this method to produce a phosphorus sulfide such as phosphorus pentasulde of the desired yellow color for all of its numerous applications since it invariably yields a yellow product with a greyish cast. Thus, while this method yields products having a color which adapt it for many applications, there are certain ones such as the oil additive art in which it is not only desirable but essential that the phosphorus sullide have a bright canary yellow color. Moreover, such a color is quite desirable from the standpoint of customer appeal and saleabihty of the product.

Therefore, it is the primary object of the instant 1n- -vention to provide a method of producing phosphorus suldes of uniform composition, which overcomes the disadvantages outlined above. More speciiically it is an object of the instant invention to provide an economically and commercially feasible method of producing continuously phosphorus suliides having a bright canary yellow color. Other objects and advantages will become apparent to those skilled in the art as the description of the invention proceeds.

l have developed an economically and commerciallyv feasible method of making phosphorus sultides having a bright canary yellow color, which represents a substantial advance in the art over the methods described earlier herein. ln accordance with the preferred embodimentof this method phosphorus and sulfur are introduced continuously into a heel of boiling phosphorus sulfide contained in a combined reactor and still wherein the exo thermic heat of the phosphorus-sulfur reaction eects continuous distillation of the resulting reaction product. Simultaneously with the phosphorus-sulfur reaction, air or oxygen is introduced continuously into the heel of boiling phosphorus suliide so as to eect improvement in the color of the reaction product.

The distillate obtained as a result of the phosphorussulfur reaction is conveyed continuously to a hot condenser where the phosphorus sulfide vapor is condensed substantially completely while the uncondensed gases and phosphorus sulfide vapors are vented to the atmosphere.

The condensed liquid phosphorus sulde is cooled further and fed continuously onto a chill roll which solidities and breaks up the product into lliakes continuously. lf desired, the phosphorus sulde from the combined reactor and still may be cooled in the condenser to a safe operating temperature and fed continuously onto the chill roll. After leaving the chill roll, the naires are ground continuously into a powder by means of a hammer mill or another equivalent pulverizing device.

As an alternative to this method, the product from the combined reactor and still, without treatrnent with air or oxygen, is condensed continuously and subjected to combined distillation and treatment with air or oxygen until the product has been converted to the desired bright canary yellow color.

As a further alternative to this method, the. phosphorus-sulfur reaction products prepared by the methods of the prior art are subjected to combined distillation and treatment with air or oxygen or to treatment with oxygen or air per se or one of the additives hereinafter mentioned (with or without heating) until the desired bright canary yellow color is obtained.

Stated broadly, the air or oxygen is introduced into the phosphorus sulfide at a rate or in an amount suficient to yield the desired yellow color. More specically, the air or oxygen is introduced at a rate or in an amount sufficient to convert aboutV 1% to about 10% and preferably from about 4% to about 8% by weight of the phosphorus sulfide into phosphorus trioxydisultide.

For a more complete understanding of the improved method of making phosphorus sultldes, reference is made to the accompanying iiow sheet which constitutes part of the instant specification.

Reference characters l and 2 represent phosphorus and sulfur feed tanks from which these reactants are continuously fed by nitrogen pressure via lines 3 and 4, re spectively, into a heel of phosphorus suliide contained in a combined reactor and still 5, the nitrogen used for this purpose being introduced into tanks l and 2 by way of lines 6 and 7, respectively.

The combined reactor and still 5 includes a still pot and in communication therewith a packed column containing porcelain Berl saddles, Pyrex glass rings and wool or equivalent materials. This combined reactor and still is provided with an outlet line S for discharging still bottoms' therefrom and a discharge line 9 for conveying the l 'distilled phosphorus sulfide vapors from the packed c ol- 'umnfse'ctionlnot shown) of the still to a hot condenser 10; it'isalso equipped with a line 5' for introducing air into Atheheel `of' phosphorus sulfide in the combined re- -facto'r and still 5.;

Y f The condenserlis providedwith a jacket Y11 having Y `an inletI line 12 for introducing aV heat exchanging medium fat a temperature ofabout 300 C. and an outlet line 13 `for discharging the heat exchanging medium-ata temperature of about 305T1C. from thefjacket. Thei'com denser is also equipped with a ventrline 14 for discharging i the inert un'condensable gas and'traces ofrphosphorus sulfide from the system, Vandra take-off line 15 for *conducting the condensed liquid phosphorus sulfide to a ooolerl.

The cooler 16 is provided with a jacket`17 having'an Y inlet'line 1S for introducingra heatrexchanging medium Y Vata temperature of about 300 C. and an outlet line 19 forY conducting the heat exchanging rnediurnatY a temperraturre of'about'BOSf C. from the jacket 17. In addition, the cooler4 16 is equipped with a discharge line 20 for 1 'conveying the cooled phosphorus sulfide into an enclosed Y f'chill wheel 21.

The `chill Wheel 21 is cooled by means ofwater or Yanother suitable medium intro-duced by line 22 and dis- .K charged therefrom by line 23; in addition, in order to avoid'combustion'of the-*phosphorus VsulfideV being flaked, c it is blanketed'by means of an inert gas such as nitrogen VVVor carbon dioxide, etc. which is introduced` by line'24 into the enclosure therefor (not shown) and discharged 'Y therefrom `by means Vof kline 25. This chill'wheel V19 is Y provided Vwith an outlet Yline 26 throughrwhich the ,aked Y phosphorus Vsulfide is conveyed to a grinding lmill 27 whereY the akesare Vground to-a finely divided state.

The lgrinding -mill 27 is purged by means of anV inert gas such as nitrogen or carbon'dioxide, etc. whichenters the rnill byline 23 and leaves by line 29, the purging be- Y ing done as a precautionary measure to avoid combustion of the phosphorus sulfide. This grinding mill is provided Ywith a line 30 for conveyingV nes to a dust collector finuously mthegrinding min ad com/erred into, powder i Y at a, rate Yof about 100 lbs. per hour. y

The phosphorus pentasulfide thus obtained had Y Y Example Il Y Y The Ypreceding.example Yrepeated but in order t0 obtain a product of'improvedf-color air waslintroduced.` continuouslyrata rate of 26 cubic feet-.per hour into'the" heel of phosphorus pentasulfde 'simultaneously with theV phosphorus and sulfur;

VVThe product obtained by V'this modified rnethodlhad Y Y melting pointrof about Y bright canary yellow color and a 280 C. vm abismos# o.

Esampialll Y 'Y Liquid phosphorus and liquid sulfur were Vcontinuously charged under nitrogen pressure Vinto a heel of 'phosphorusVVV` pentasulfde yinv.substantially the proportions 'requirerd't-o `V yield the pentasulde anda yellowish grey` prodllt `was' Y Ycollected continuously asa distillate. Then', theffeeding f of phosphorus and sulfur was.discontinuedand.the'dis-' tillation continued: bythe external applicationaof heat.'`

No improvement in color ofthe Vproduct was obtained.

Approximately 1% by Yweight (basis heel of phosphorus pentasulde.) of boric oxide'was added tothe heel'andVY the distillationvcontinued for a VperiodV of about rhour,V

. The phosphorus pentasulfde product recoveredmfrom the operation had a bright canaryyellow color, thus`dem0nl' `strati'ng theveiective'nessofboric oxide in improving the color of this product.

in likemannr phosphorusrheptasulde and phosphorusV sesquisulide havingabright yellow colorgcan be producedY in acontinuous mannerVV by continuously Yfeeding and the reactants in theproportionsrequired to yieldqthese products Vand by Y,operating at atemperatureequivalent to the boilingfpoints-ofgthe'heptasulfide and 'sesquisultidq Y respectively,` at the'foperating pressure. Y Y

in the production of phosphorus pentasulfde accord-Y ance witn theV instant invention, phosphorus Vand sulfur'- are continuously fed to Va combined reaction;andfdistil#` lation zone where they'arer'r'eakcted together Vina heel-of 31 from which a portion of the inert purging gas is vented Y into thelatmosphere by line 32; The grinding Vrnill27 isy Vfurther provided with a liuer33 for conveyingV the final product to the' packaging plant 34.

Y The following are Vspecific examples of the method of Y carrying out the instant invention .employingV the system illustrated in the accompanying drawing.

Y o Example] The'combined reactor and still Y5 was charged Vwith the reaction product'and at a temperature at least 'equiva Vlent to the boiling .pointk of.- the reaction product Vat the operating pressure. Whenoperatiug at atmospheric pres# f sure, ythe reaction temperature used inthe Vforrnatic'm of phosphorus penta'sulfidefshould'ffall `substantially inthe range of about 505 C. to 525 C., whereas in the pro-,

" vduction of phosphorus sesquisulfide and phosphorus'hep- Y Vabout 150 lbs. of phosphorus pentasulfide and then heated Y to a temperatureof about 515 C. so as to provide a fluid:

heel or reactlon medium for the phosphorus sulfideV reac- Y Liquid phosph'o'rusand-'liquid sulfur, bothunder nitro-V gen'pre'ssure, lwere introduced continuously into the above heel of phosphorus pentasulldeat flow rates correspond.-

ringL to 3l lbs: and.80 Vlbs., p`er hour, respectively, jsaid Y. owrates being suflicient to Vmaintain a yreaction tem- Y perature of about 515 C. The exothermic heat produced The distillate including the inert'g'aswas conveyed con- `as a result ofV the reaction Vbetween the phosphorus and y sulfur caused the resulting phosphorus pentasullide to dis till Ycontinuously/from the combined reactor andstill 5.

` duction rate.

tasulfide, the reaction temperatureshouldffall withinthe f Y ranges of fromabout 400 C.; to about420 Gand-from n about 520 C.'to about 535 C., respectively. Y

T he ,reactants'are introduced continuously into the'heel of phosphorusV sulfide at a rate producing areactionitemperature atleast; equivalent Vto the boiling'pointfofthe v phosphorus sulfide, thus insuring continuous distillationrof this product substantially las rapidly as it is Yformed. lf. .A

desired, thereaction heatV may beysupplementedV Vby the application' of external'heatingmeans lto thegcornbined reactor and still.

In the production of cooling action maintainv theY desired Air is introduced continuously into theheel Vofthephosphorus sulfide simultaneously withy theV phosphorus and t 'Y Y sulfur at a rate suicient to produce V.a pri'idu'ct'having.Y the desired bright yellow color. Inlproducng a brightY yellow phosphorus pentasullide,V1 air is'introduced intothe heel of phosphorus pentasulfidewith phosphorus aud'sulfurat a ratesucient to convert'. from 1 to.10%1and pref-V erably from Itito 8% by Yweight'ofvthc distillcdphosphortw Y Va grey-'i` ishV yellow color and a meltingV point Iofrabout 280 C. Y Y

Y phosphorus Vsesquisulfdeor.vphoskV 'Y phorus heptasulfrde, the heatY of reaction in excess offthat requiredtor distillation is dissipated inthecondenser' by. i using VaV distillation rate greater thanthe productionrate g and permitting a portionof the ,condensate'gtogrreturn from the condenser to the reactorfstill pot; afnduby temperature and'proY-f pentasulfide into P45406 in accordance with the following equation:

Fisio-F302* Ristori-F332 In place of air, additives such as oxygen, free-oxygencontaining gases, phosphorus trioxydisulde, oxides of boron, phosphorus, sulfur and nitrogen, and materials which under the conditions of phosphorus sulfide distillation form trioxydisulfide may be employed to produce phosphorus sulfides having a bright yellow color.

Somewhat lower feed rates for the additive can be used in the production of a bright yellow colored phosphorus sesquisulfide or phosphorus heptasulfide since these products do not present a color improvement problem that is as serious as is encountered in the manufacture of phosphorus pentasulfide.

Instead of introducing the additive into the heel of phosphorus sulfide, the distilled product may be condensed and then subjected to combined distillation and treatment with the additive or to treatment with the additive per se (with or without heating) to form a light colored product.

The product leaving the combined reaction and distillation zone is cooled to condense the phosphorus sulfide, the temperature used varying with the particular phosphorus sulde being produced. In the case of phosphorus pentasulfide, the product from the combined reaction and distillation zone is cooled to a temperature of about 500 C. or to a lower temperature above its solidiication point to effect substantially complete condensation of the phosphorus pentasulfide.

The condensed phosphorus pentasulfide at a temperature of about 500 C. liows into a cooler where it is cooled to about 300 to 350 C. However, this temperature is not fixed since it varies with the phosphorus sulfide being produced, the only limitation being that the liquid phosphorus sullide should not be cooled to a temperature preventing free ow thereof onto the chill wheel. This cooling step may be omitted if the product is cooled to a safe operating temperature in the condensation zone.

The liquid phosphorus sulfide is discharged continuously from the condenser or cooler onto a chill wheel and converted into flakes which are introduced continuously into a grinding mill where they are ground to a finely divided state.

The flaking and grinding operations are preferably carried out in the presence of a dry inert atmosphere, but the invention is by no means restricted thereto since this is merely a desirable precautionary measure designed to prevent decomposition of the product by air and moisture.

The products of the instant invention are suitable for use in organic synthesis and in a number of commercial applications such as anticorrosive agents and antioxidants for oils, in the manufacture of extreme pressure and lubricants, match compositions and vulcanized rubber.

What I claim is:

1. The method of preparing bright yellow colored phosphorus sullides which comprises introducing free oxygen-containing gas into a mass of darkly colored phosphorus sulde while subjecting the resulting product to distillation to separate said phosphorus sulfide in the forrn of a product having a bright canary yellow color, said free oxygen-containing gas being employed in an amount sufcient to produce said color improvement.

2. The method of preparing bright yellow colored phosphorus pentasulfide which comprises introducing free oxygen-containing gas into a mass of darkly colored phosphorus pentasulfide while subjecting the resulting product to distillation to separate said phosphorus pentasullide in the form of a product having a bright canary yellow color, said reagent being employed in an amount sufficient to produce said color improvement.

3. The method of preparing bright yellow colored phosphorus pentasulfide which comprises introducing free oxygen-containing gas into a mass of darkly colored phosphorous pentasulfide while subjecting the resulting product to distillation to separate said phosphorus pentasulde in the form of a product having a bright canary yellow color, said free oxygen-containing gas being employed in an amount sufficient to convert about 1% to about 10% of said phosphorus pentasulfide into phosphorus trioxydisulfide.

4. The method of preparing bright yellow colored phosphorous sullides which comprises continuously introducing phosphorus, sulfur and free oxygen-containing gas into a boiling mass consisting of a darkly colored phosphorus sulfide, and thereby electing a continuous reaction between said phosphorus and said sulfur and continuous distillation of said reaction product in the form of a bright canary yellow colored product, said reactants being introduced continuously into said boiling mass in substantially proportions calculated to yield said phosphorus sulfide and at a rate maintaining said mass in a boiling condition, and said free oxygen-containing gas being introduced at a rate sufiicient to convert about 1% to about 10% of said distilled reaction product into phosphorus trioxydisulde.

5. The method of preparing bright yellow colored phosphorus sulfides which comprises continuously introducing phosphorus, sulfur and free oxygen-containing gas into a boiling mass consisting of a darkly colored phosphorus sultide, and thereby eiecting a continuous reaction between said phosphorus and said sulfur and continuous distillation of said reaction product in the form of a bright canary yellow colored product, said reactants being introduced continuously into said boiling mass in substantially the proportions calculated to yield said phosphorus sulfide and at a rate maintaining said mass in a boiling condition, and said free oxygen-coutainig gas being introduced at a rate suicient to convert about 4% to about 8% of said distilled reaction product into phosphorus trioxydisulfide.

6. The method of preparing bright yellow colored phosphorus pentasulfide which comprises continuously introducing phosphorus, sulfur, and free oxygen-containing gas into a boiling mass consisting of darkly colored phosphorus pentasullide, and thereby effecting a continuous reaction between said phosphorus and said sulfur and continuous distillation of said reaction product in the form of a bright canary yellow colored product, said reactants being introduced continuously into said boiling mass in substantially the proportions calculated to yield said phosphorus pentasulide and at a rate maintaining the said mass in a boiling condition, and said free oxygencontaining gas being introduced at a rate suicient to convert about 4% to about 8% of said distilled reaction product into phosphorus trioxydisulde.

References Cited in the file of this patent UNITED STATES PATENTS 2,569,128 Jones Sept. 25, 1951 FOREIGN PATENTS 420,832 France Dec. 5, 1910 

1. THE METHOD OF PREPARING BRIGHT YELLOW COLORED PHOSPHORUS SULFIDES WHICH COMPRISES INTRODUCING FREE OXYGEN-CONTAINING GAS INTO A MASS OF DARKLY COLORED PHOSPHORUS SULFIDE WHILE SUBJECTING THE RESULTING PRODUCT TO DISTIALLATION TO SEPARATE SAID PHOSPHORUS SULFIDE IN THE FORM OF A PRODUCT HAVING A BRIGHT CANARY YELLOW COLOR, SAID FREE OXYGEN-CONTAINING GAS BEING EMPLOYED IN AN AMOUNT SUFFICIENT TO PRODUCE SAID COLOR IMPROVEMENT. 